1. Field of the Invention
The present invention relates to a hypoid gear structure, and more particularly, relates to a hypoid gear structure having an excellent abnormal-sound prevention property.
2. Description of the Related Art
A technique for using a hypoid gear is a motor-driven power steering device is known. In such a technique, the hypoid gear is disposed as a decelerating mechanism between a rotation axis of an electric motor for providing an auxiliary force for steering and an output axis of a steering system. The rotation axis of the electric motor and the output axis of the steering system are coupled with each other by the hypoid gear structure which functions as a decelerating mechanism.
One problem of the above conventional motor-driven power steering device is that it is difficult to appropriately set a backlash produced at the engaging portion of gears in the hypoid gear structure.
For example, Japanese Laid-Open Publication No. 7-232651 discloses that such a backlash produced at the engaging portion of the gears can be appropriately controlled by adjusting the position at which a hypoid ring gear is attached in the vertical direction.
In the conventional hypoid gear structure described in the above-mentioned publication, the engagement between the hypoid ring gear and a hypoid pinion gear is adjusted so that an appropriate backlash is obtained at a correct meshed position between the hypoid ring gear and the hypoid pinion gear. This allows for smooth engagement therebetween. However, if the hypoid gear structure receives a vibration and the like from the side of the tires (from the road surface), an abnormal sound such as a tooth striking sound may be generated due to a backlash even if the backlash is within an appropriate range.
The hypoid gear structure of this invention includes: a hypoid ring gear disposed coaxially with a rotation axis; and hypoid pinion gear provided with a rotation axis of an electric motor and engaging with the hypoid ring gear, wherein the hypoid ring gear includes a first toothed portion disposed on the inner side and a second toothed portion disposed on the outer side, and one of the first toothed portion and the second toothed portion is urged by a spring to press the hypoid pinion gear.
In one embodiment of the invention, the one of the first toothed portion and the second toothed portion is shaped so as to be in a correct engagement with the hypoid pinion gear in a state where the one of the first toothed portion and the second toothed portion is meshed with the hypoid pinion gear with the spring being bent.
In another embodiment of the invention, the first toothed portion is urged by the spring to press the hypoid pinion gear, and the first toothed portion is coupled with the second toothed portion via the spring.
In still another embodiment of the invention, an outer periphery of the first toothed portion is shaped so as to be kept apart from an inner periphery of the second toothed portion.
In still another embodiment of the invention, the spring is a plate spring having a ring portion, and a rotation regulating portion for regulating the rotation of the plate spring with respect to the second toothed portion is formed at an inner periphery of the plate spring.
In still another embodiment of the invention, the first toothed portion is made of a resin.
In still another embodiment of the invention, the first toothed portion is formed on a pedestal disposed on the spring by insert molding.
Alternatively, the hypoid gear structure of this invention includes: a hypoid ring gear disposed coaxially with a rotation axis; and a hypoid pinion gear provided with a rotation axis of an electric motor and engaging with the hypoid ring gear, wherein the hypoid ring gear includes a concave portion, and the concave portion is filled with a vibration-absorbing material.
Alternatively, the hypoid gear structure of this invention includes: a hypoid ring gear disposed coaxially with a rotation axis; and a hypoid pinion gear provided with a rotation axis of an electric motor and engaging with the hypoid ring gear, wherein the hypoid ring gear includes concave portions formed alternately in a predetermined direction.
In one embodiment of the invention, the concave portions are filled with a vibration-absorbing material.
In another embodiment of the invention, the tooth flank of the first toothed portion and the tooth flank of the second toothed portion form a continuous tooth flank in a state where the one of the first toothed portion and the second toothed portion is meshed with the hypoid pinion gear with the spring being bent.
Thus, the invention described herein makes possible the advantage of providing a hypoid gear structure which can reduce the generation of an abnormal sound such as a tooth striking sound due to a vibration received from the road surface.
These and other advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the following detailed description with reference to the accompanying figures.